1. Field of the Invention
The invention relates to the drive with continuous movement in synchronism in the same direction of several parallel, at least pulling cables of a transportation installation comprising in operation at least one vehicle connected in line to the said at least pulling cables.
2. Description of the Prior Art
It is already known that one of the problems encountered in the construction of a transportation installation having several aerial supporting/pulling cables comprising at least one vehicle connected to all these supporting/pulling or pulling cables, resides in the necessity of driving the cables in perfect synchronism.
One solution has been proposed in French Patent No. 2 430 901 which recommends perfectly identical loops of cable, a connection of each vehicle to the cables by two pairs of grippers in order to form a rigid quadrilateral imposing the synchronous drive of the cables and a mechanical, hydraulic or electrical differential device in the vicinity of the drive motors. However, this solution was not satisfactory since it required absolutely identical loops of cable, which is never the case in practice, on account of the constraints of the trajectories which it is not always possible to respect.
European Patent No. 93.680 also teaches that it is necessary to provide two absolutely identical loops of cable, to form a rigid quadrilateral for the connection of the vehicles to the cables and to drive the cables by two strictly identical d.c. motors supplied from the same electrical supply source providing constant power by virtue of an electrical differential device. French Patent No. 2 552 716 recommends how one can construct such an electrical differential by incorporating in series resistances of fixed value in the induced circuits of the two motors, supplied in parallel from the same d.c. source. Here too, it has been found that it is not possible in practice to produce two identical loops of cable. Furthermore, the electrical differential produced by the resistances has proved to be the subject of resonance phenomena and one drawback thereof is that it is not possible to control the electrical supply of each motor. It has thus been found in practice that the cabins suspended from the cables are sometimes subject to swinging movements of great amplitude in a transverse plane with respect to the cables, which is detrimental to the comfort and safety of the passengers. Moreover, tests carried out with the differential device according to French Patent No. 2 552 726 on installations having a winding course have shown that such a device is absolutely inadequate for ensuring a synchronous drive of the two cables.